The present invention relates to an ultrasonic trocar having a paracentetic section which is designed to penetrate the abdominal wall and to which ultrasonic vibration may be transmitted.
Disposable trocars are mainly used at present as devices that guide medical instrument into the abdominal cavity of a patient. U.S. Pat. No. 5,314,417 discloses a trocar of this type, which has a needle and a tubular sheath. The needle is pointed at its distal end and can penetrate the abdominal wall. The needle is inserted in the tubular sheath. The pointed distal end of the needle is a blade-shaped knife-edge. It is at the knife-edge that the needle penetrates the abdominal wall of the patient.
Most disposable trocars incorporate a safety shield mechanism. The mechanism works as a safety guard when the trocar is manipulated to pierce the abdominal wall with the needle. The mechanism has a safety shield. The safety shield contacts and covers the pierced part of the wall when the distal end of the needle penetrates into the abdominal cavity. Thus, the mechanism prevents the needle from further moving into the abdominal cavity, and thus preventing the tissues present in the abdominal cavity from being damaged.
Another type of a trocar is disclosed in U.S. Pat. 5,267,965. The needle of this trocar has a star-shaped distal end. It is at the star-shaped distal end that the needle penetrates the abdominal wall of the patient.
Reusable trocars are known. A reusable trocar is washed and sterilized after every use and is used again. Developed as reusable trocars are ultrasonic trocars, each having a paracentetic section to which ultrasonic vibration can be transmitted. The paracentetic section receives ultrasonic vibration during the use of the ultrasonic trocar. This enables the doctor to pass the paracentetic section through the abdominal wall with a relatively small force.
The paracentetic section of the needle of a typical ultrasonic trocar is shaped like a triangular pyramid. After every use of the ultrasonic trocar, the paracentetic section is sterilized with gas or heat so that the trocar may be used again.
The conventional trocars of the various types described above are disadvantageous in the following respects.
The disposable trocar has a safety shield that prevents the needle from further moving into the abdominal cavity. Having the safety shield, the disposable trocar is more complex in structure than otherwise. In other words, the disposable trocar has more parts, inevitably increasing the manufacturing cost. To make matters worse, the disposable trocar cannot be sterilized with gas or heat after it has been used once. It cannot be used again at all.
In the case of the disposable trocar disclosed in U.S. Pat. No. 5,314,417, the knife-edge becomes dull after use. Were the trocar used again, the doctor should apply a large force to pass the paracentetic section through the abdominal wall. Hence, the paracentetic section might move too deep into the abdominal cavity, possibly damaging the organs which exist in the abdominal cavity and which need not be treated at all.
In the case of conventional ultrasonic trocar, the paracentetic section, shaped like a triangular pyramid, makes a triangular incision hole in the abdominal wall. The incision hole is relatively large and possibly left open even after the ultrasonic trocar is removed from the abdominal wall. As a consequence, it may take a long time to heal the tissues in the abdominal wall. If the paracentetic section is a conical one, as the case may be, it will be more difficult for the doctor to pass this section through the abdominal wall than in the case where the section is shaped like a triangular pyramid. This is because the conical paracentetic section receives higher resistance while being passed through the abdominal wall than the triangular pyramidal one.
The present invention has been made in consideration of the above. Its object is to provide an ultrasonic trocar that can be reusable, that can be manufactured at low cost, and that has a paracentetic section easy to pass through the abdominal wall, and that does not delay the healing of the tissues present in the abdominal wall.
To attain the object, the present invention provides an ultrasonic trocar, which has a tubular sheath and a needle unit inserted in the tubular sheath and designed to penetrate the abdominal wall while vibrated with ultrasonic waves. The ultrasonic trocar is characterized in that the needle unit has a substantially pyramidal paracentetic section at a distal end, and the paracentetic section has two cutting surfaces formed by cutting diagonally opposing two ridges, and two sharp cutting edges for cutting living tissues. The sharp cutting edges are provided at the two other diagonally opposing ridges and positioned symmetrically with respect to an axis of the needle unit.
To set the tubular sheath in an incision made in the abdominal wall, ultrasonic vibration is transmitted to the needle unit. The paracentetic section of the needle unit, which is vibrating, is brought into contact with the abdominal wall. At least the cutting edges at the distal portion of the two opposing ridges of the paracentetic section cut the abdominal wall easily, making an incision in the abdominal wall and the peritoneum. As the paracentetic section of the needle unit is inserted into the incision, the cutting edges of the paracentetic section gradually cut the abdominal wall. As a result, the paracentetic section is inserted into the abdominal cavity. The paracentetic section, which is the thickest part of the needle unit, receives a larger force than any other part of needle unit. Hence, the cutting edges, which constitute the thickest part of the unit, cut the abdominal wall efficiently. The distal end portion of the insertion section of the tubular sheath can therefore be smoothly inserted into the incision made in the abdominal wall. In the process of incising the abdominal wall, the curved surfaces of the paracentetic section do not damage the tissues existing in the abdominal wall. This helps to heal the tissue in the abdominal wall within a relatively short time.
The distal end part of the needle unit has curved surfaces and two ridges. The ridges are symmetrical with respect to the axis of the needle unit, each defined by at least two curved surfaces. Edges for cutting living tissues are provided at the distal parts of the ridges and at the proximal, or thickest parts of the ridges. Thus, the present invention can provide an ultrasonic trocar which can used again and again, helping to decrease medical cost, which can be smoothly inserted into the incision made in the abdominal wall and which does not damage the tissues in the abdominal wall.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.